This invention relates to intravascular ultrasonic imaging, particularly to data processing techniques for improving image perception.
With the increasing frequency (above 40 MHz) ultrasonic signals, blood speckles appear more prominently in ultrasonic intravascular images. The speckles are sufficiently bright to lower the contrast between blood and tissue, making it harder for physicians to determine the true boundaries based on a single frame images.
Most blood speckle reduction algorithms use either spatial or temporal information only, which is insufficient to determine the characteristic. See, for example, B. Olstad, "Noise reduction in ultrasound images using multiple linear regression in a temporal context", SPIE, vol. 1451, pp.269-281, 1991; Olstad, et al., "Analysis and measurement of temporal tissue variations", U.S. Pat. No. 5476096, 1995; and Karaman, et al., "An adaptive speckle suppression filter for medical ultrasonic imaging", IEEE Trans. Med. Imag., vol.14, pp.283-292, 1995.
Some algorithms have attempted to combine spatial and temporal filtering. However, they are so complex and cumbersome that processing cannot be realized in real-time with known technology. See, for example, Evans, et al., "Biased Motion-Adaptive Temporal Filtering for Speckle Reduction in Echocardiography", IEEE Trans. Med. Imag., vol.15, pp.39-50, 1996.
Tissue tends to be static over short periods of time. Blood cells move rapidly so blood speckles are randomly scattered. However, due to the fast cardiac motion and speckling nature of the high frequency ultrasound signals, it is difficult to differential blood and tissue without the consideration of additional information, such as spatial properties. What is needed is a near real-time technique for suppression of spurious dynamic artifacts.